This is a copy of the same question I posed in the 6.8L V10 portion of the forum. Hoping the added visibilty here in the general Super Duty section will get me more feedback.

Let me start by saying this is NOT a request for help to get fog lights and high beams to stay on at the same time. That seems to be a common question based on search. This is something different.

With engine running and all lights off, here's my situation:

1. Turn on parking lights. No issue, works as expected.
2. With parking lights on, turn on fog lights by pulling out on the factory headlight switch. No issue, works as expected.
3. With parking lights and fog lights on, turn on low beam headlights. No issue, works as expected.
4. Turn on high beams, low beams and fog lights turn off as expected. No issue, works as expected.
5. Turn off high beams, low beams and fog lights come back on. But high beams stay on as well.
6. From this point, If I turn off the fog lights, high beams and fog lights both turn off and I'm left with low beams on only. If I turn the fog lights back on, they will light without the high beams coming back on.

Also, I found if I have the fog lights on, low beam headlights off, and pull on the stalk to flash the high beams, once I release the high beams, fog lights and high beams remain on. I have to turn the fog lights off and then the high beams will then also turn off. So the low beams seemingly have nothing to do with my issue.

From my owner's manual, doesn't appear to me that there are any relays involved in the various circuits? So I'm not sure really where to go looking to get this fixed.

For what it's worth, I am not running any LED's. My headlights are Sylvania Silverstar and the fog lights are H10 42w bulbs.

Any help or advice is GREATLY appreciated. Would like to get this fixed ASAP since winter has arrived and day lights hours are relatively short now.

 

I have a Taurus and had similar thing happen about drove me nuts. Finally traced it down to a mouse had nicked 1 wire in harness when it corroded and broke the relays would back feed to each other. Check your ground points. Be interesting to see how you get this figured out. If you leave the foglamps off is everything normal?

 

Have you checked the high beam relay to see if its getting powered by some short or feed back from the fog lamp relay?

I think you'll need a wiring diagram for the lamp circuits of your model year truck. Then you can figure out where the power is on and off at set times. It took me awhile to find the wiring diagram for my F350 as I was trying to figure out why the foglamps didn't have power after replacing non working bulbs. Side story: Turned out that on my truck, the fog lamps only fully connected to receive power with the truck key switch in run or start. I was use to the F150 having foglamps on when selected by the headlamp switch, go figure. I also had a previous owner that fell in love with wire taps. I have removed 10 of those vile things since owning the truck, and I am still running across them.

There are a few different relays on the circuit. Maybe see if the high beams deactivate after turning the key to off (which may kill power to the fog lamps if your relay system is similar to my 07). If the highs stay on then you may have a relay before that set of relays that isn't working right.